CMake: Make directbase/pandabase INTERFACE libraries

They export no code, and are really only used to contain several
preprocessor macros relevant to their respective packages. On
Windows, they're a problem: MSVC doesn't generate a .lib when
compiling a .dll that exports nothing.

cmake/macros/BuildMetalib.cmake

@@ -30,24 +30,29 @@ function(target_link_libraries target)
       set_property(TARGET "${target}" APPEND PROPERTY INCLUDE_DIRECTORIES "${include_directories}")
       set_property(TARGET "${target}" APPEND PROPERTY INTERFACE_INCLUDE_DIRECTORIES "${include_directories}")
 
-      # Also build with the same BUILDING_ macros, because these will all end
-      # up in the same library.
-      set(compile_definitions "$<$<BOOL:$<TARGET_PROPERTY:${library},IS_COMPONENT>>:$<TARGET_PROPERTY:${library},COMPILE_DEFINITIONS>>")
-      set_property(TARGET "${target}" APPEND PROPERTY COMPILE_DEFINITIONS "${compile_definitions}")
-
       # Libraries are only linked transitively if they aren't components.
       # Unfortunately, it seems like INTERFACE_LINK_LIBRARIES can't have
       # generator expressions on an object library(?) so we resort to taking
       # care of this at configuration time.
       if(TARGET "${library}")
-        get_target_property(is_component "${library}" IS_COMPONENT)
+        get_target_property(target_type "${library}" TYPE)
+        if(NOT target_type STREQUAL "INTERFACE_LIBRARY")
+          get_target_property(is_component "${library}" IS_COMPONENT)
+        else()
+          set(is_component OFF)
+        endif()
       else()
         # This is a safe assumption, since we define all component libraries
         # before the metalib they appear in:
         set(is_component OFF)
       endif()
 
-      if(NOT is_component)
+      if(is_component)
+        # Also build with the same BUILDING_ macros, because these will all end
+        # up in the same library.
+        set(compile_definitions "$<TARGET_PROPERTY:${library},COMPILE_DEFINITIONS>")
+        set_property(TARGET "${target}" APPEND PROPERTY COMPILE_DEFINITIONS "${compile_definitions}")
+      else()
         set_property(TARGET "${target}" APPEND PROPERTY INTERFACE_LINK_LIBRARIES "${library}")
       endif()
     else()

direct/CMakeLists.txt

@@ -15,7 +15,7 @@ add_subdirectory(src/motiontrail)
 add_subdirectory(src/showbase)
 
 set(P3DIRECT_COMPONENTS
-  p3dcparser p3deadrec p3directbase
+  p3dcparser p3deadrec
   p3interval p3motiontrail p3showbase)
 if(HAVE_PYTHON)
   list(APPEND P3DIRECT_COMPONENTS p3distributed)

direct/src/directbase/CMakeLists.txt

@@ -6,10 +6,8 @@ set(P3DIRECTBASE_HEADERS
   directbase.h directsymbols.h
 )
 
-# Not worth compositing sources, there's really only one.
-add_component_library(p3directbase NOINIT
-  ${P3DIRECTBASE_HEADERS} ${P3DIRECTBASE_SOURCES})
-target_link_libraries(p3directbase panda)
+# Yes, INTERFACE: don't build it, there's no code!
+add_library(p3directbase INTERFACE)
+target_link_libraries(p3directbase INTERFACE panda)
 
-install(TARGETS p3directbase DESTINATION lib)
 install(FILES ${P3DIRECTBASE_HEADERS} DESTINATION include/panda3d)

panda/src/pandabase/CMakeLists.txt

@@ -6,8 +6,8 @@ set(P3PANDABASE_SOURCES
   pandabase.cxx
 )
 
-add_component_library(p3pandabase ${P3PANDABASE_HEADERS} ${P3PANDABASE_SOURCES})
-target_link_libraries(p3pandabase p3dtool)
+# Yes, INTERFACE: don't build it, there's no code!
+add_library(p3pandabase INTERFACE)
+target_link_libraries(p3pandabase INTERFACE p3dtool)
 
-install(TARGETS p3pandabase DESTINATION lib)
 install(FILES ${P3PANDABASE_HEADERS} DESTINATION include/panda3d)